1. Field of the Invention
The present invention relates to contact lenses that are used in treating myopia, and more particularly, to contact lenses that are shaped to provide gradual altering of the patient""s cornea during continued wear to reshape the cornea to reduce the myopic condition.
2. Description of the Related Art
Many people experience difficulties with their vision due to a number of possible conditions. The most common vision problem is a condition known as myopia or nearsightedness. Myopia is a common condition where an eye cannot focus on far-away objects because the cornea of the eye is curved too steeply (i.e., where the radius of curvature of the cornea is smaller than normal) to provide adequate focusing at the retina of the eye. Another condition is known as hyperopia or farsightedness. With hyperopia, the eye cannot focus on near objects because the curvature of the cornea of the eye is too flat to provide adequate focusing at the retina of the eye. Another common problem is astigmatism, where unequal curvature of one or more refractive surfaces of the cornea prevents light rays from focusing clearly at one point on the retina, resulting in blurred vision.
Myopia is a condition for which no entirely suitable permanent treatment has been developed. One approach to correcting myopia is through surgical reshaping of the cornea. However, such surgical procedures have not been entirely safe and there is some question; as to the permanency of the surgically altered lens shape.
Another approach to treating some or all of these conditions is to alter the corneal shape by wearing contact lenses which are designed to continually exert pressure on selected locations of the cornea to gradually force or mold the cornea into the desired normal corneal curvature. A retainer lens is then worn on a part-time basis to prevent the cornea from returning to its previously deformed shape. This method of treatment is commonly referred to as orthokeratology (referred to herein as xe2x80x9cortho-kxe2x80x9d). The success of any treatment by ortho-k is dependent upon the shape and structure of the contact lens.
For example, conventional contact lenses with a longer central radius of curvature than the central radius of the cornea are known to change the shape of the cornea by compressing the surface at its apex. This reshaped cornea has a lengthened radius of curvature in its central zone, which serves to improve myopia.
Ortho-k has been performed in some form or another since the early 1970s. There are three factors that impact the effectiveness and desirability of ortho-k procedures and lenses. The first factor is the time needed to achieve a desired visual correction. Unfortunately, the time needed to achieve a desired visual correction using known ortho-k techniques and lenses has been a serious problem, although recent efforts have actually reduced this correction time from several years to several months. The second factor is the amount of myopia that can be corrected using ortho-k. Prior known ortho-k techniques and lenses were limited to a reduction of 2 to 5 diopters of myopia. The third factor is the amount of time that the correction would xe2x80x9choldxe2x80x9d before degrading (known as the maintenance period). Known ortho-k techniques and lenses were variable in the length of the maintenance period. To prolong this maintenance period, the patient would have to wear a retainer lens.
U.S. Pat. No. 5,963,297 to Reim discloses an ortho-k contact lens having four correction zones, listed from the center of the lens to the outer periphery: an optical zone, a fitting zone, an alignment zone, and a peripheral zone. This patent purports that its ortho-k contact lens provides a number of benefits, which if true, do provide some improvements over the previously available contact lens.
Notwithstanding the improvements provided by U.S. Pat. No. 5,963,297 to Reim, there remains a need for a contact lens that can be used for ortho-k, which provides increased reduction of myopia, requires a shorter correction time, and provides a longer maintenance period.
It is an object of the present invention to provide an ortho-k contact lens that provides increased reduction of myopia.
It is another object of the present invention to provide an ortho-k contact lens that provides a shorter correction time.
It is yet another object of the present invention to provide an ortho-k contact lens that provides a longer maintenance period.
The objects of the present invention may be achieved by providing an apparatus and method for correcting a myopic condition in a patient""s eye. In accordance to a method according to the present invention, a contact lens is fitted to a cornea of a patient""s eye, the contact lens having a plurality of zones that includes a facilitate zone. The facilitate zone is utilized to redistribute cornea tissue to cause the cornea to have a flattened central portion surrounded by a steep mid-peripheral ring.
In accordance to an apparatus according to the present invention, a contact lens is provided having a base curve portion of the lens having a longer radius of curvature than a central portion of a cornea, a fitting curve portion of the lens circumscribing and coupled to the base curve portion, a facilitate curve portion of the lens circumscribing and coupled to the fitting curve portion, and an alignment curve portion of the lens circumscribing and coupled to the facilitate curve portion.